The present invention relates to integrated circuits, and more particularly to fuses and diodes.
Some CMOS integrated circuit processes have tried to form a one-time programmable element called a xe2x80x9cpoly fuse.xe2x80x9d A poly fuse may comprise a Co, Ti or other metal layer formed on a polysilicon layer, such as a LPCVD poly film. The LPCVD poly film may be doped/implanted with a contaminant to lower the bulk resistivity. The metal layer is silicided with some of the poly layer, and the result is a silicided polysilicon layer (also called a xe2x80x9cpolysilicidexe2x80x9d) over an unsilicided polysilicon layer.
Some processes xe2x80x9cprogramxe2x80x9d a poly fuse by passing a sufficiently high current through the silicided polysilicon (fuse material). The current heats the silicide such that the temperature rises above a certain critical temperature where the silicide changes phase and increases in resistance. The change of phase may increase the density and be accompanied by a clustering or agglomeration of the silicided doped polysilicon molecules, which can form voids in the silicide layer, and thus increase the resistance substantially. The phase change may reduce one or more geometric dimensions of the silicided polysilicon. In some cases, the reduced dimensions may cause the silicided polysilicon film to separate at or physically move away from a junction of highest heat dissipation, which can be ascertained by post-processing physical analysis. The amount of silicide agglomeration may vary from fuse to fuse. The process of applying current to change the silicided polysilicon from a relatively low resistance state to a relatively high resistance state may be referred to as xe2x80x9cprogrammingxe2x80x9d the fuse.
The invention recognizes that a standard CMOS integrated circuit process does not have the capability of creating diodes that are sufficiently isolated from the substrate, unless additional mask and implant steps are added. The invention also recognizes that one-time programmable elements, such as silicided poly fuses, may be used as programmable elements in a wide range of integrated circuit applications.
An integrated polysilicon fuse and diode circuit and methods of making the same are provided in accordance with the present invention. The integrated polysilicon fuse and diode combination described herein may be implemented in a programmable cross point fuse array. The integrated poly fuse and diode may advantageously be used in a nonvolatile, random access memory (RAM) cell/element. The poly fuse and diode described herein are less expensive to manufacture than other types of nonvolatile memory elements, such as FERAM and MRAM, which may require adding process steps to a standard CMOS process. As an example, the poly fuse and diode may be used to store a serial or part number of a device, such as a computer mouse.
Compared to other types of diodes that may be used in a memory array with fuses as the memory element, the polysilicon diode described herein may be isolated from a substrate and from other devices, use less area on a substrate, and cost less to manufacture.